Film casting machine



Jan. 17, E, J, BARNES 1,894,845

FILM CASTING MACHINE Filed Feb. 21, 1931 2 Sheets-Sheet l /Afvsn fa fr my# M Jan. 17, 1933. E, BARNES 1,894,845

FILM CASTING MACHINE Filed Feb. 2l, 1951 2 Sheets-Sheet 2 Mwmw Patented Jan. 17, 1933 UNITED STATES PATENT OFFICE EDWARD JOHN BARNES, OF SAWSTON, ENGLAND, ASSIGNOR TO SPICERS LIMITED, OF LONDON, ENGLAND, A BRITISH COMPANY FILM CASTING MACHINE Application filed February 21, 1931, Serial No This invention comprises improvements in or relating to iilm casting and similar machines and especially to machines of the known band or drum type.

In the band type of iilm-casting machines, a solution of cellulose acetate, Celluloid or other ester or ether of cellulose (in a volatile solvent) is extruded in a thin layer from a casting box on to an endless band passing around two rotating drums. One of said drums (the forward drum) has a. portion exposed to the open air, but the remainder of the forward drum and of the band and the rear drum are all enclosed in a casing. As the band moves forward away from the casting box, it passes into the casing, wherein the solvent is caused to evaporate by the action of heat, a film of cellulose ester being left on the band, whence it is continuously removed at some convenient subsequent point (conveniently from the lower exposed part of the forward drum). i In the drum type of casting machine the endless band is replaced by a single rotating drum, onto which the cellulosic solution is eX- truded, and from which the finished film is removed in a manner similar to that in the case of the band-machine described above.

Within the hood or casing of the machine there are provided means for assisting the evaporationy of the solvent, and means for condensing the solvent vapours, the condensate being collected and removed from the casing for treatment in a suitable recovery plant.

It is important for the economical operation of a film-casting machine that the maximum possible quantity of solvent should be recovered, and it is the object of this invention to provide means whereby the escape of solvent vapours from the casing may be avoided. 'V

This invention provides a method of preventing the escape of solvent vapours from film casting and like machines, which consists in applying to one or any of the orifices in the machine casing through which vapour solvent might escape, a gas pressure which is equal to or greater than the total pressure of gas and vapour within the casing.

. 517,821, and in Great Britain March 4, 1930.

sufficient to prevent the escape of solvent vapours from said casing.

According to a feature of the invention the aforesaid apparatus may comprise an air duct terminating opposite said orifice (or a plurality of air ducts each terminating opposite j one of said orifices) which is connected to a blower or like source of air pressure. Preferably the mouth of the air duct is flattened and expanded into the form of a narrow slot.

In the preferred form of the invention the stream of air from the mouth of the air duct is directed on to the band, near the point at which it emerges from the orifice in the machine casing, in a substantially radial direction (i. e. in a direction substantially parallel to the plane of said orifice). Y This has the eect of providing, opposite the orifice in the machine casing, what may be termed as a wall of air at a pressure greater than that of the solvent vapour within the casing, which eifectually prevents the escape of vapour therefrom, whilst at the same time reducing as far'as possible the quantity of air which is actually7 blown into the machine casing.

It will be understood-that the pressure of solvent vapour within the machine casing will depend upon the speed and thickness at which the film is cast, and according to a further feature of the invention regulating means are provided within the air ducts so as to permit of adjustment of the quantity of air delivered at the orice per unit of time according to the pressure of the solvent vapour in the casing. Inone embodiment of the invention baliie plates are provided at or near the mouth of the air duct in order to distribute the air pressure evenly over the area of the orifices.

A practical embodiment of the invention will now be described by way of example fto with reference to the accompanying drawin in which igure 1 is an elevation, partly broken away, of the machine,

F lgure 2 is a part plan and section taken along the line 2-2 in Figure 1 and looking in the direction of the arrows, and

Figure 3 is an enlarged sectional view of that portion of the machine where the film is stripped from the band.

Like reference numerals indicate like parts throughout the drawings.

The machine comprises a copper band 13 passing around two drums 12 and 14, which rotate in the direction of the arrows. The

surface of the band remote from the drums I carries a layer of gelatin. The dope e. g., a solution of cellulose acetate in acetone containin suitable plasticizers, is deposited on the ge afin coated upper lap of the band from the casting box 11, which is located above the water-cooled drum 12. The dope fed by ravity to the casting box 11. Convenienty the casting box of thedouble-casting type described in British specification No. 281,803. Considering now an element of the band which has just received a coating of dope from the casting box, this element passes immediately afterwards through a narrow slot-like orifice (not shown) into the machine casing 15. In the casing the band passes successively through bridges7 where it is heated by means of steam heated pipes, so as to drive off the solvent and deposit the cellulose acetate on the band in the form of a film i and through condensers in which the solvent vapours are condensed and recovered. The present invention is not concerned with the constructional details of the heating pipes and condensers, which are therefore not illustrated in the drawings. The length of the casing 15 is generally of the order of from to 40 feet. After passing round the second roller 14, which is totally enclosed in the machine casing, the element of the band under consideration enters the lower lap of the machine casing in which it is once again submitted to the action of the steam heating pipes and condensers. The band together with the film adhering thereto, leaves the condenser 16 by means of the orifice 17 and the film 18 is stripped continuously from that portion of the band which is in contact with the exposed portion of the drum 12 by means of the roller 19.

The edges of the film are then trimmed, 'and the film is led over a series of rollers in a casing through which a current of hot air is passed to remove further traces of solvent from-it, and to render it fit for reeling.

As will be understood from the foregoing description, the machine is totally enclosed except for that portion of the band on which the dope is cast and from which the film is removed, i. e. that portion which is passing round the right hand side of the drum 12. The only orifice through which solvent vapours can escape from the machine is the orifice 17 No solvent vapours will be given off from that part of the band which has just received the dope from the casting box 11, and which has not yet entered the casing 15,- as this portion of the band is in Contact with the water-cooled drum 12. In order however to protect this part of the band from the effects of moist air a removable wooden casi-ng 20, having a glass top through which the casting operation may be observed, is fitted loosely over theupper portion of the drum 12.

In order to prevent the escape of solvent vapours from the orifice 17 warm air, e. g. at a temperature of from 650 to o C., is blown on to the surface of the band near the point at which it emerges from the orifice 17 (which is conveniently lined with felt strips 26). The air is directed on to the surface of the band from the conduit 21, which is connected to the main air supply 22 from a blower.

24 is a regulator to vary the amount of airA delivered per unit of time through the conduit 21. The mouth of the conduit 21 is flattened, and has the form of a narrow slot 25. The upper lip 27 of this orifice is bent downwards, but the lower' lip 23 is bent upwards at an angle which is conveniently made adjustable, so that the stream of air is directed on to the surface of the band in a radial direction across the mouth of the orifice 17, as indicated by the arrows in Fig!y ure 3. Owing to this arrangement, hardly any of the air actually enters the machine casing, but the air pressure outside the orifice 17 nevertheless effectually prevents the escape of acetone vapour therefrom. Bale`- plates 28 in the mouth of the conduit serve tok distribute the air pressure evenly over the orifice 17.

I claim 1. The combination with the machine casing'4 of a film casting machine of the kind in which evaporation of the solvent within the machine casing is effected solely by means of heat, said casing having at least one orifice through which solvent vapor might normally escape; of means to apply to each escape orifice in said casing a gas pressure which is sufficient to prevent the escape of solvent vapors from that orifice` under conditions such that substantially no gas can enter the machine cas-vr ing through that orifice.A

2. The combination with the machine casing of a film casting machine of the kind in which evaporation of the solvent within the machine casing is effected solely by means of a current of air across the mouth of the orilice at a pressure not less than the fluid pressure Within the casing and in a direction substantially parallel to the plane of the orifice.

3. The combination with the machine casing of a film casting machine of the kind in which evaporation oi the solvent Within the machine casing is effected solely by means of heat, said casing having at least one orifice through Which solvent vapor might normally escape, of an air duct terminating opposite each escape orifice and arranged to supply a current of air at a temperature of about 650- C. across the mouth of the orice at a pressure not less than the fluid pressure Within the casing and in a direction substantially parallel to the plane of the oriiice.

4. The combination with the machine casing of a lilm casting machine of the kind in which evaporation of the solvent Within the machine casing is eilected solely by means of heat, said casing having at least one orifice through Which solvent vapor might normally escape, of an air duct terminating opposite each escape orifice and arranged to supply a current of air across the mouth of the oriiice at a pressure not less than the iuid pressure Within the casing and in a direction substantially parallel to the plane of the oriice, said air duct having a mouth which is expanded into the form of a narrow slot.

5. A film casting machine comprising in combination a machine casing, a conveyor surface movable Within said casing, said casing have oriiices to permit of the conveyor entering and leaving the casing, means to apply to the conveyor a solution in a volatile solvent of a film-forming composition, heating means located Within the casing to evaporate the solvent from the conveyor, means located outside the machine casing to strip from the conveyor the iilm left thereon by the evaporation of said solvent, and means to apply to the conveyor, at the oriiice Where the conveyor emerges from the machine casing, a stream of gas in a direction which is substantially normal to the conveyor at the point of emergence and under conditions of pressure such that substantially no gas can enter the machine casing through that orifice.

6. A film casting machine comprising in combination a machine casing, a travelling conveyor surface movable Within said casing, said casing having orilices to permit of the conveyor entering and leaving the casing, means to apply to said conveyor a solution in a volatile solvent of a hlm-forming composition, heating means located Within the casing to evaporate the solvent from the conveyor, means located outside the machine casing to strip from the conveyor the lilm left thereon by the evaporation of said solvent, and located at the orifice Where the conveyor emerges from the machine casing, an air duct arranged to direct a stream of air onto the surface of the conveyor at the point of emergence in a direction substantially normal to the conveyor at that point and under conditions of pressure such that substantially no air can enter the machine casing through that orifice.

7. A iilm casting machine comprising in combination, a machine casing, a travelling conveyor surface movable Within said casing, said casing having orii'ices to permit of the conveyor entering and leaving the casing, means to apply to said conveyor a solution in a volatile solvent of a hlm-forming composition, heating means located Within the casing to evaporate the solvent from the conveyor, means located outside the machine casing to strip from the conveyor` the film left thereon by the evaporation oi said solvent, and located at the orifice at which the conveyor emerges from the machine casing, an air duct having a mouth which is expanded into the form or" a narrowT slot-like orifice and arranged to direct a stream of air onto the sur- Jface of the conveyor lat that point of emergence in a direction substantially normal to the conveyor and under conditions of pressure such that substantially no air can enter the machine casing through that orifice.

ln testimony whereof l aiix my signature.

EDJVARD JOHN BARNES. 

